`define INSN_NOP 8'b00000000
`define INSN_RST 8'b11xxx111
`define INSN_RET 8'b110x1001 // 1 = RETI, 0 = RET
+`define INSN_CALL 8'b11001101
+`define INSN_JP_imm 8'b11000011
+`define INSN_JPCC_imm 8'b110xx010
+
+`define INSN_cc_NZ 2'b00
+`define INSN_cc_Z 2'b01
+`define INSN_cc_NC 2'b10
+`define INSN_cc_C 2'b11
`define INSN_reg_A 3'b111
`define INSN_reg_B 3'b000
reg [7:0] rdata, wdata; /* Read data from this bus cycle, or write data for the next. */
reg rd = 1, wr = 0, newcycle = 1;
- reg [7:0] tmp; /* Generic temporary reg. */
+ reg [7:0] tmp, tmp2; /* Generic temporary regs. */
reg [7:0] buswdata;
assign busdata = buswr ? buswdata : 8'bzzzzzzzz;
registers[ 9] <= 0;
registers[10] <= 0;
registers[11] <= 0;
+ ie <= 0;
+ rd <= 1;
+ wr <= 0;
+ newcycle <= 1;
+ state <= 0;
+ cycle <= 0;
end
always @(posedge clk)
case (state)
`STATE_FETCH: begin
- if (wr)
- buswdata <= wdata;
- if (newcycle)
+ if (newcycle) begin
busaddress <= {registers[`REG_PCH], registers[`REG_PCL]};
- else
+ buswr <= 0;
+ busrd <= 1;
+ end else begin
busaddress <= address;
- buswr <= wr;
- busrd <= rd;
+ buswr <= wr;
+ busrd <= rd;
+ if (wr)
+ buswdata <= wdata;
+ end
state <= `STATE_DECODE;
end
`STATE_DECODE: begin
rdata <= busdata;
newcycle <= 0;
cycle <= 0;
- end else
+ end else begin
if (rd) rdata <= busdata;
+ cycle <= cycle + 1;
+ end
buswr <= 0;
busrd <= 0;
wr <= 0;
end
endcase
end
+ `INSN_CALL: begin
+ case (cycle)
+ 0: begin
+ `EXEC_INC_PC;
+ `EXEC_NEXTADDR_PCINC;
+ rd <= 1;
+ end
+ 1: begin
+ `EXEC_INC_PC;
+ `EXEC_NEXTADDR_PCINC;
+ rd <= 1;
+ end
+ 2: begin
+ `EXEC_INC_PC;
+ end
+ 3: begin
+ address <= {registers[`REG_SPH],registers[`REG_SPL]} - 1;
+ wdata <= registers[`REG_PCH];
+ wr <= 1;
+ end
+ 4: begin
+ address <= {registers[`REG_SPH],registers[`REG_SPL]} - 2;
+ wdata <= registers[`REG_PCL];
+ wr <= 1;
+ end
+ 5: begin
+ `EXEC_NEWCYCLE; /* do NOT increment the PC */
+ end
+ endcase
+ end
+ `INSN_JP_imm,`INSN_JPCC_imm: begin
+ case (cycle)
+ 0: begin
+ `EXEC_INC_PC;
+ `EXEC_NEXTADDR_PCINC;
+ rd <= 1;
+ end
+ 1: begin
+ `EXEC_INC_PC;
+ `EXEC_NEXTADDR_PCINC;
+ rd <= 1;
+ end
+ 2: begin
+ if (!opcode[0]) begin // i.e., JP cc,nn
+ /* We need to check the condition code to bail out. */
+ case (opcode[4:3])
+ `INSN_cc_NZ: if (registers[`REG_F][7]) begin `EXEC_NEWCYCLE; end
+ `INSN_cc_Z: if (!registers[`REG_F][7]) begin `EXEC_NEWCYCLE; end
+ `INSN_cc_NC: if (registers[`REG_F][4]) begin `EXEC_NEWCYCLE; end
+ `INSN_cc_C: if (!registers[`REG_F][4]) begin `EXEC_NEWCYCLE; end
+ endcase
+ end
+ end
+ 3: begin
+ `EXEC_NEWCYCLE;
+ end
+ endcase
+ end
default:
$stop;
endcase
casex (opcode)
`INSN_LD_reg_imm8:
case (cycle)
- 0: cycle <= 1;
+ 0: begin end
1: case (opcode[5:3])
- `INSN_reg_A: begin registers[`REG_A] <= rdata; cycle <= 0; end
- `INSN_reg_B: begin registers[`REG_B] <= rdata; cycle <= 0; end
- `INSN_reg_C: begin registers[`REG_C] <= rdata; cycle <= 0; end
- `INSN_reg_D: begin registers[`REG_D] <= rdata; cycle <= 0; end
- `INSN_reg_E: begin registers[`REG_E] <= rdata; cycle <= 0; end
- `INSN_reg_H: begin registers[`REG_H] <= rdata; cycle <= 0; end
- `INSN_reg_L: begin registers[`REG_L] <= rdata; cycle <= 0; end
- `INSN_reg_dHL: cycle <= 2;
+ `INSN_reg_A: begin registers[`REG_A] <= rdata; end
+ `INSN_reg_B: begin registers[`REG_B] <= rdata; end
+ `INSN_reg_C: begin registers[`REG_C] <= rdata; end
+ `INSN_reg_D: begin registers[`REG_D] <= rdata; end
+ `INSN_reg_E: begin registers[`REG_E] <= rdata; end
+ `INSN_reg_H: begin registers[`REG_H] <= rdata; end
+ `INSN_reg_L: begin registers[`REG_L] <= rdata; end
+ `INSN_reg_dHL: begin /* Go off to cycle 2 */ end
endcase
- 2: cycle <= 0;
+ 2: begin end
endcase
`INSN_HALT: begin
/* Nothing needs happen here. */
/* XXX Interrupts needed for HALT. */
end
`INSN_LD_HL_reg: begin
- case (cycle)
- 0: cycle <= 1;
- 1: cycle <= 0;
- endcase
+ /* Nothing of interest here */
end
`INSN_LD_reg_HL: begin
case (cycle)
- 0: cycle <= 1;
+ 0: begin end
1: begin
case (opcode[5:3])
`INSN_reg_A: registers[`REG_A] <= tmp;
`INSN_reg_H: registers[`REG_H] <= tmp;
`INSN_reg_L: registers[`REG_L] <= tmp;
endcase
- cycle <= 0;
end
endcase
end
end
`INSN_LD_reg_imm16: begin
case (cycle)
- 0: cycle <= 1;
+ 0: begin /* */ end
1: begin
case (opcode[5:4])
`INSN_reg16_BC: registers[`REG_C] <= rdata;
`INSN_reg16_HL: registers[`REG_L] <= rdata;
`INSN_reg16_SP: registers[`REG_SPL] <= rdata;
endcase
- cycle <= 2;
end
2: begin
case (opcode[5:4])
`INSN_reg16_HL: registers[`REG_H] <= rdata;
`INSN_reg16_SP: registers[`REG_SPH] <= rdata;
endcase
- cycle <= 0;
end
endcase
end
`INSN_LD_SP_HL: begin
case (cycle)
- 0: begin
- cycle <= 1;
- registers[`REG_SPH] <= tmp;
- end
- 1: begin
- cycle <= 0;
- registers[`REG_SPL] <= tmp;
- end
+ 0: registers[`REG_SPH] <= tmp;
+ 1: registers[`REG_SPL] <= tmp;
endcase
end
`INSN_PUSH_reg: begin /* PUSH is 16 cycles! */
case (cycle)
- 0: begin
- {registers[`REG_SPH],registers[`REG_SPL]} <=
- {registers[`REG_SPH],registers[`REG_SPL]} - 1;
- cycle <= 1;
- end
- 1: begin
- {registers[`REG_SPH],registers[`REG_SPL]} <=
- {registers[`REG_SPH],registers[`REG_SPL]} - 1;
- cycle <= 2;
- end
- 2: cycle <= 3;
- 3: cycle <= 0;
+ 0: {registers[`REG_SPH],registers[`REG_SPL]} <=
+ {registers[`REG_SPH],registers[`REG_SPL]} - 1;
+ 1: {registers[`REG_SPH],registers[`REG_SPL]} <=
+ {registers[`REG_SPH],registers[`REG_SPL]} - 1;
+ 2: begin /* type F */ end
+ 3: begin /* type F */ end
endcase
end
`INSN_POP_reg: begin /* POP is 12 cycles! */
case (cycle)
- 0: begin
- cycle <= 1;
- {registers[`REG_SPH],registers[`REG_SPL]} <=
- {registers[`REG_SPH],registers[`REG_SPL]} + 1;
- end
+ 0: {registers[`REG_SPH],registers[`REG_SPL]} <=
+ {registers[`REG_SPH],registers[`REG_SPL]} + 1;
1: begin
case (opcode[5:4])
`INSN_stack_AF: registers[`REG_F] <= rdata;
endcase
{registers[`REG_SPH],registers[`REG_SPL]} <=
{registers[`REG_SPH],registers[`REG_SPL]} + 1;
- cycle <= 2;
end
2: begin
case (opcode[5:4])
`INSN_stack_DE: registers[`REG_D] <= rdata;
`INSN_stack_HL: registers[`REG_H] <= rdata;
endcase
- cycle <= 0;
end
endcase
end
`INSN_LDH_AC: begin
case (cycle)
- 0: cycle <= 1;
- 1: begin
- cycle <= 0;
- if (opcode[4])
- registers[`REG_A] <= rdata;
- end
+ 0: begin /* Type F */ end
+ 1: if (opcode[4])
+ registers[`REG_A] <= rdata;
endcase
end
`INSN_LDx_AHL: begin
case (cycle)
- 0: cycle <= 1;
+ 0: begin /* Type F */ end
1: begin
- cycle <= 0;
if (opcode[3])
registers[`REG_A] <= rdata;
{registers[`REG_H],registers[`REG_L]} <=
`INSN_ALU8: begin
if ((opcode[2:0] == `INSN_reg_dHL) && (cycle == 0)) begin
/* Sit on our asses. */
- cycle <= 1;
end else begin /* Actually do the computation! */
case (opcode[5:3])
`INSN_alu_ADD: begin
`INSN_NOP: begin /* NOP! */ end
`INSN_RST: begin
case (cycle)
- 0: cycle <= 1;
- 1: cycle <= 2;
- 2: cycle <= 3;
- 3: begin
- cycle <= 0;
- {registers[`REG_SPH],registers[`REG_SPL]} <=
- {registers[`REG_SPH],registers[`REG_SPL]}-2;
- end
+ 0: begin /* type F */ end
+ 1: begin /* type F */ end
+ 2: begin /* type F */ end
+ 3: {registers[`REG_SPH],registers[`REG_SPL]} <=
+ {registers[`REG_SPH],registers[`REG_SPL]}-2;
endcase
end
`INSN_RET: begin
case (cycle)
- 0: cycle <= 1;
- 1: begin
- cycle <= 2;
- registers[`REG_PCL] <= rdata;
- end
- 2: begin
- cycle <= 3;
- registers[`REG_PCH] <= rdata;
- end
+ 0: begin /* type F */ end
+ 1: registers[`REG_PCL] <= rdata;
+ 2: registers[`REG_PCH] <= rdata;
3: begin
- cycle <= 0;
{registers[`REG_SPH],registers[`REG_SPL]} <=
{registers[`REG_SPH],registers[`REG_SPL]} + 2;
if (opcode[4]) /* RETI */
end
endcase
end
+ `INSN_CALL: begin
+ case (cycle)
+ 0: begin /* type F */ end
+ 1: tmp <= rdata; // tmp contains newpcl
+ 2: tmp2 <= rdata; // tmp2 contains newpch
+ 3: begin /* type F */ end
+ 4: registers[`REG_PCH] <= tmp2;
+ 5: begin
+ {registers[`REG_SPH],registers[`REG_SPL]} <=
+ {registers[`REG_SPH],registers[`REG_SPL]} - 2;
+ registers[`REG_PCL] <= tmp;
+ end
+ endcase
+ end
+ `INSN_JP_imm,`INSN_JPCC_imm: begin
+ case (cycle)
+ 0: begin /* type F */ end
+ 1: tmp <= rdata; // tmp contains newpcl
+ 2: tmp2 <= rdata; // tmp2 contains newpch
+ 3: {registers[`REG_PCH],registers[`REG_PCL]} <=
+ {tmp2,tmp};
+ endcase
+ end
+ default:
+ $stop;
endcase
state <= `STATE_FETCH;
end
endcase
endmodule
-
-`timescale 1ns / 1ps
-module TestBench();
- reg clk = 0;
- wire [15:0] addr;
- wire [7:0] data;
- wire wr, rd;
- reg [7:0] rom [2047:0];
-
- initial $readmemh("rom.hex", rom);
- always #10 clk <= ~clk;
- GBZ80Core core(
- .clk(clk),
- .busaddress(addr),
- .busdata(data),
- .buswr(wr),
- .busrd(rd));
- assign data = rd ? rom[addr] : 8'bzzzzzzzz;
-endmodule
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